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From hospital bed to seabed

CT scanning has already revolutionised medicine, now it is driving innovation deep beneath the waves.

Godfrey Hounsfield: inventor of the CT scanner

Godfrey Hounsfield left school at 16 with a report detailing his “intellectual retardation”. He could not have known that he would go on to invent the CT scanner, revolutionise medicine and win a Nobel prize.

And he certainly could never have imagined that almost half a century later, his scanners would be put to work more than a kilometre under the sea.

The move to reengineer the technology for use under the waves was made by Tracerco, a UK-based business which helps oil and gas companies improve their operations.

“Shell came to us because they needed to find out what was causing a restriction in a pipe at a field in the Gulf of Mexico,” recalls Lee Robins, Head of Subsea Services of Tracerco.

“We were already looking at the possibility of using CT scanning technology to inspect pipes for corrosion, then we realised we could use it to see what was inside the pipes too. It was the perfect solution.”

The technology, which is not yet a routine part of inspections but could become one, is essentially the same as that used in hospitals.

The patient, or subsea pipeline, sits in the middle of a doughnut-shaped machine. On one side is a source of radiation and on the other are detectors. The detectors pick up variations in the radiation level, which depends on the density of the substances it travels through.

The doughnut shape allows both the source and the detectors to move in a circle around the patient or pipeline, with images taken from a multitude of angles. A computer can then take the data and translate it into an image.

The technology has three big advantages over other pipe inspection techniques: firstly, there is no need to stop production in the pipe when it is being inspected and secondly, it can be scanned without stripping off any external coatings or coverings. This makes the technique quicker and cheaper than other, more traditional, external methods – especially in deep water. The third advantage is that its accuracy means it can spot corrosion.

Shell was the first company to use Tracerco’s “Discovery” scanner. Engineers believed that a natural build-up of wax was likely to be responsible for the restricted flow in a pipe in the Gulf of Mexico. The proposed solution was to shut down the pipeline and flush it through with a mix of chemicals - a process expected to cost around $10 million.

Before interrupting operations, Discovery was sent down to make sure.

Yet when the results were analysed the scans revealed a surprise. Instead of wax, the restriction was mainly being caused by something with a higher density: scale. Flushing the pipe with that original mix of chemicals would have made no difference at all.

A second benefit of the investigation was the measurement of the pipe wall thickness. It revealed the pipe was much thicker than anticipated, a finding that could double its expected life.

Eric Caldwell, a Shell materials and corrosion engineer who worked on the project, said: “When I got the first scans back I thought: ‘Whoa! We can get this quality of data?’ It was far better than we had even hoped for. This really could be a game-changing innovation for the industry, something that could make it both safer and more efficient.”